The invention relates to call routing via a moving base station in a radio system, and to a radio system.
Known aircraft telephone systems operate like closed radio networks. In these systems, aircraft passengers and crew can use terminals in an aircraft to call to subscribers in a terrestrial telephone network. The calls made are charged, for example, on a credit card. FIG. 1 of the attached drawing shows in a block diagram the structure of an aircraft telephone system. A call made from a telephone system 10 located in an aircraft is routed via a satellite 12 to a ground earth station GES, whose transceiver TRX forwards the call via a switch SW to the subscriber through a public switched telephone network PSTN. A few simultaneous calls can be connected and routed from an aircraft.
FIG. 2 of the attached drawing shows a simplified block diagram of the Global System for Mobile communications (GSM). A mobile station MS is connected over a radio path to a base transceiver station BTS, in FIG. 2 to BTS1. A base station controller BSC controls the operation of the base transceiver stations BTS dedicated to it. A base station sub-system BSS comprises the base station controller BSC and base transceiver stations BTS controlled by the base station controller BSC. A mobile services switching centre MSC usually controls several base station controllers BSC. The mobile services switching centre MSC is connected to other mobile services switching centres and the GSM network is connected via a gateway mobile services switching centre GMSC to other networks such as a public switched telephone network PSTN, another land mobile network PLMN or an ISDN network. The operation of the entire system is controlled by an operation and maintenance centre OMC.
The subscriber information of a mobile station MS is stored permanently in the home location register HLR of the system and temporarily in the visitor location register VLR of the area in which the mobile station MS is currently located. During location update, the information stating the visitor location register VLR, whose area the mobile station MS is in, is updated to the home location register HLR. The location information of the mobile station MS is stored in the visitor location register VLR with an accuracy of the location area LA. The geographical area controlled by the visitor location register is divided into one or several location areas LA, which can each have one or several base transceiver stations BTS. Each base transceiver station BTS continuously transmits information for all of the mobile stations on its broadcast channel. This information includes the base station identity code BSIC, the location area identifier LAI and information about the frequencies of the neighboring base stations to be measured by the mobile stations MS. When the mobile station MS moves so that the received location area identifier changes, the mobile station starts the location update for the network.
The location information in the subscriber information of the mobile station is used, for example, for routing calls. In a mobile communications system of the GSM type, a mobile terminating call is routed to the mobile services switching centre MSC of the current location area of the mobile station MS according to the location information in the home location register HLR. On the basis of the information in the visitor location register VLR, a paging message is sent for the mobile station MS on the paging channels of all of the base transceiver stations BTS of the current location area. After the mobile station MS has responded, the call is connected on a channel of that base transceiver station BTS through which the mobile station MS responded to the paging message. A mobile communications network identifies the mobile station MS on the basis of the international mobile subscriber identity IMSI stored on the SIM card of the mobile station MS and/or on the basis of the temporary mobile subscriber identity TMSI given by the visitor location register VLR to the mobile station MS.
Cellular radio networks such as the GSM system described above are designed only for terrestrial use. Therefore, it is not possible to use a mobile station of terrestrial type in an aircraft, especially as it is forbidden by the authorities. Also the moving nature of an aircraft presents a problem. In the aircraft telephone system described above, the problem is the fact that the system can only route a few simultaneous calls. Additionally, the calls are charged on a credit card and passengers cannot receive calls during the flight.
The object of this invention is to enable call routing between a moving target, such as an aircraft or a ship, and a public land mobile communications network.
This is achieved by using a method according to the invention characterized by what is stated in the independent claim 1. Specific embodiments of the invention are presented in the dependent claims.
The invention relates also to a radio system characterized by what is stated in the independent claim 7.
The invention is based on the idea of routing the calls between the mobile services switching centre and the ground earth station via a dedicated control unit in a mobile communications system. Between the ground earth station and a moving cell, such as an aeronautical cellular network (ACNW) in an aircraft, the calls are routed via a satellite.
The advantage in this kind of call routing is that it is suitable for routing calls from subscribers of any cellular networks even when the terrestrial networks are not compatible. The method can also be used, for example, in routing data or signaling messages. An additional benefit is the fact that charging is handled by the subscriber""s operator.
The method according to the invention also has the advantage of minimizing signaling in the network. The reachability of the subscriber is also made better.
The advantage of the radio system according to the invention is that the call relaying capacity can be arranged to be sufficient.